/*
 * %W% %E%
 *
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util.prefs;

import java.util.Map;
import java.util.TreeMap;
import java.util.StringTokenizer;
import java.io.ByteArrayOutputStream;
import java.util.logging.Logger;

/**
 * Windows registry based implementation of  <tt>Preferences</tt>.
 * <tt>Preferences</tt>' <tt>systemRoot</tt> and <tt>userRoot</tt> are stored in 
 * <tt>HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Prefs</tt> and 
 * <tt>HKEY_CURRENT_USER\Software\JavaSoft\Prefs</tt> correspondingly.
 *
 * @author  Konstantin Kladko
 * @version %I%, %G%
 * @see Preferences
 * @see PreferencesFactory
 * @since 1.4
 */

class WindowsPreferences extends AbstractPreferences{
        
    /** 
     * Logger for error messages 
     */
    private static Logger logger;

    /** 
     * Windows registry path to <tt>Preferences</tt>'s root nodes.         
     */    
    private static final byte[] WINDOWS_ROOT_PATH 
                               = stringToByteArray("Software\\JavaSoft\\Prefs");

    /** 
     * Windows handles to <tt>HKEY_CURRENT_USER</tt> and 
     * <tt>HKEY_LOCAL_MACHINE</tt> hives.
     */
    private static final int HKEY_CURRENT_USER = 0x80000001;
    private static final int HKEY_LOCAL_MACHINE = 0x80000002;
    
    /** 
     * Mount point for <tt>Preferences</tt>'  user root.
     */
    private static final int USER_ROOT_NATIVE_HANDLE = HKEY_CURRENT_USER;
    
    /** 
     * Mount point for <tt>Preferences</tt>'  system root.
     */
    private static final int SYSTEM_ROOT_NATIVE_HANDLE = HKEY_LOCAL_MACHINE;
    
    /**
     * Maximum byte-encoded path length for Windows native functions,
     * ending <tt>null</tt> character not included.
     */
    private static final int MAX_WINDOWS_PATH_LENGTH = 256;
    
    /** 
     * User root node.
     */
    static final Preferences userRoot =  
         new WindowsPreferences(USER_ROOT_NATIVE_HANDLE, WINDOWS_ROOT_PATH);
    
    /** 
     * System root node.
     */
    static final Preferences systemRoot =  
        new WindowsPreferences(SYSTEM_ROOT_NATIVE_HANDLE, WINDOWS_ROOT_PATH);
        
    /*  Windows error codes. */
    private static final int ERROR_SUCCESS = 0;
    private static final int ERROR_FILE_NOT_FOUND = 2;
    private static final int ERROR_ACCESS_DENIED = 5;
    
    /* Constants used to interpret returns of native functions    */
    private static final int NATIVE_HANDLE = 0;
    private static final int ERROR_CODE = 1;
    private static final int SUBKEYS_NUMBER = 0;
    private static final int VALUES_NUMBER = 2;
    private static final int MAX_KEY_LENGTH = 3;
    private static final int MAX_VALUE_NAME_LENGTH = 4;
    private static final int DISPOSITION = 2;
    private static final int REG_CREATED_NEW_KEY = 1;
    private static final int REG_OPENED_EXISTING_KEY = 2;
    private static final int NULL_NATIVE_HANDLE = 0;
    
    /* Windows security masks */
    private static final int DELETE = 0x10000;
    private static final int KEY_QUERY_VALUE = 1;
    private static final int KEY_SET_VALUE = 2;
    private static final int KEY_CREATE_SUB_KEY = 4;
    private static final int KEY_ENUMERATE_SUB_KEYS = 8;
    private static final int KEY_READ = 0x20019;
    private static final int KEY_WRITE = 0x20006;
    private static final int KEY_ALL_ACCESS = 0xf003f;

    /**
     * Initial time between registry access attempts, in ms. The time is doubled
     * after each failing attempt (except the first).
     */
    private static int INIT_SLEEP_TIME = 50;

    /**
     * Maximum number of registry access attempts.
     */
    private static int MAX_ATTEMPTS = 5;

    /**
     * BackingStore availability flag.
     */
    private boolean isBackingStoreAvailable = true;
    
    /** 
     * Java wrapper for Windows registry API RegOpenKey()
     */
    private static native int[] WindowsRegOpenKey(int hKey, byte[] subKey,
                                                         int securityMask);
    /**
     * Retries RegOpenKey() MAX_ATTEMPTS times before giving up.
     */
    private static int[] WindowsRegOpenKey1(int hKey, byte[] subKey,
                                                      int securityMask) {
        int[] result = WindowsRegOpenKey(hKey, subKey, securityMask);
        if (result[ERROR_CODE] == ERROR_SUCCESS) { 
            return result;
        } else if (result[ERROR_CODE] == ERROR_FILE_NOT_FOUND) {
            logger().warning("Trying to recreate Windows registry node " +
            byteArrayToString(subKey) + " at root 0x" + 
            Integer.toHexString(hKey) + ".");
            // Try recreation
            int handle = WindowsRegCreateKeyEx(hKey, subKey)[NATIVE_HANDLE];
            WindowsRegCloseKey(handle);
            return WindowsRegOpenKey(hKey, subKey, securityMask);
        } else if (result[ERROR_CODE] != ERROR_ACCESS_DENIED) {
            long sleepTime = INIT_SLEEP_TIME;
            for (int i = 0; i < MAX_ATTEMPTS; i++) {
            try {
                Thread.sleep(sleepTime);
            } catch(InterruptedException e) {
                return result;
            }
            sleepTime *= 2;
            result = WindowsRegOpenKey(hKey, subKey, securityMask);
            if (result[ERROR_CODE] == ERROR_SUCCESS) { 
                return result;
            }
            }
        }
        return result;                
    }    
    
     /** 
     * Java wrapper for Windows registry API RegCloseKey()
     */
    private static native int WindowsRegCloseKey(int hKey);
    
    /** 
     * Java wrapper for Windows registry API RegCreateKeyEx()
     */
    private static native int[] WindowsRegCreateKeyEx(int hKey, byte[] subKey);
    
    /**
     * Retries RegCreateKeyEx() MAX_ATTEMPTS times before giving up.
     */
    private static int[] WindowsRegCreateKeyEx1(int hKey, byte[] subKey) {
        int[] result = WindowsRegCreateKeyEx(hKey, subKey);
        if (result[ERROR_CODE] == ERROR_SUCCESS) { 
                return result;
            } else {    
                long sleepTime = INIT_SLEEP_TIME;
                for (int i = 0; i < MAX_ATTEMPTS; i++) {
                try {
                    Thread.sleep(sleepTime);
                } catch(InterruptedException e) {
                    return result;
                }
                sleepTime *= 2;
                result = WindowsRegCreateKeyEx(hKey, subKey);
                if (result[ERROR_CODE] == ERROR_SUCCESS) { 
                return result;
                }
            }
        }
        return result;                
    }
    /** 
     * Java wrapper for Windows registry API RegDeleteKey()
     */
    private static native int WindowsRegDeleteKey(int hKey, byte[] subKey);
    
    /** 
     * Java wrapper for Windows registry API RegFlushKey()
     */
    private static native int WindowsRegFlushKey(int hKey);
    
    /**
     * Retries RegFlushKey() MAX_ATTEMPTS times before giving up.
     */
    private static int WindowsRegFlushKey1(int hKey) {
        int result = WindowsRegFlushKey(hKey);
        if (result == ERROR_SUCCESS) { 
                return result;
            } else {    
                long sleepTime = INIT_SLEEP_TIME;
                for (int i = 0; i < MAX_ATTEMPTS; i++) {
                try {
                    Thread.sleep(sleepTime);
                } catch(InterruptedException e) {
                    return result;
                }
                sleepTime *= 2;
                result = WindowsRegFlushKey(hKey);
                if (result == ERROR_SUCCESS) { 
                return result;
                }
            }
        }
        return result;                
    }

    /** 
     * Java wrapper for Windows registry API RegQueryValueEx()
     */
    private static native byte[] WindowsRegQueryValueEx(int hKey, 
                                                              byte[] valueName);    
    /** 
     * Java wrapper for Windows registry API RegSetValueEx()
     */
    private static native int WindowsRegSetValueEx(int hKey, byte[] valueName, 
                                                         byte[] value);
    /**
     * Retries RegSetValueEx() MAX_ATTEMPTS times before giving up.
     */
    private static int WindowsRegSetValueEx1(int hKey, byte[] valueName, 
                                                         byte[] value) {
        int result = WindowsRegSetValueEx(hKey, valueName, value); 
        if (result == ERROR_SUCCESS) { 
                return result;
            } else {    
                long sleepTime = INIT_SLEEP_TIME;
                for (int i = 0; i < MAX_ATTEMPTS; i++) {
                try {
                    Thread.sleep(sleepTime);
                } catch(InterruptedException e) {
                    return result;
                }
                sleepTime *= 2;
                result = WindowsRegSetValueEx(hKey, valueName, value); 
                if (result == ERROR_SUCCESS) { 
                return result;
                }
            }
        }
        return result;                
    }    

    /** 
     * Java wrapper for Windows registry API RegDeleteValue()
     */
    private static native int WindowsRegDeleteValue(int hKey, byte[] valueName);
    
    /** 
     * Java wrapper for Windows registry API RegQueryInfoKey()
     */
    private static native int[] WindowsRegQueryInfoKey(int hKey);
    
    /**
     * Retries RegQueryInfoKey() MAX_ATTEMPTS times before giving up.
     */
    private static int[] WindowsRegQueryInfoKey1(int hKey) {
        int[] result = WindowsRegQueryInfoKey(hKey);
        if (result[ERROR_CODE] == ERROR_SUCCESS) { 
                return result;
            } else {    
                long sleepTime = INIT_SLEEP_TIME;
                for (int i = 0; i < MAX_ATTEMPTS; i++) {
                try {
                    Thread.sleep(sleepTime);
                } catch(InterruptedException e) {
                    return result;
                }
                sleepTime *= 2;
                result = WindowsRegQueryInfoKey(hKey);
                if (result[ERROR_CODE] == ERROR_SUCCESS) { 
                return result;
                }
            }
        }
        return result;                
    }

    /** 
     * Java wrapper for Windows registry API RegEnumKeyEx()
     */
    private static native byte[] WindowsRegEnumKeyEx(int hKey, int subKeyIndex, 
                                      int maxKeyLength);

    /**
     * Retries RegEnumKeyEx() MAX_ATTEMPTS times before giving up.
     */
    private static byte[] WindowsRegEnumKeyEx1(int hKey, int subKeyIndex, 
                                      int maxKeyLength) {
        byte[] result = WindowsRegEnumKeyEx(hKey, subKeyIndex, maxKeyLength);
        if (result != null) { 
                return result;
            } else {    
                long sleepTime = INIT_SLEEP_TIME;
                for (int i = 0; i < MAX_ATTEMPTS; i++) {
                try {
                    Thread.sleep(sleepTime);
                } catch(InterruptedException e) {
                    return result;
                }
                sleepTime *= 2;
                result = WindowsRegEnumKeyEx(hKey, subKeyIndex, maxKeyLength);
                if (result != null) { 
                return result;
                }
            }
        }
        return result;                
    }    
    
    /** 
     * Java wrapper for Windows registry API RegEnumValue()
     */
    private static native byte[] WindowsRegEnumValue(int hKey, int valueIndex, 
                                      int maxValueNameLength);
    /**
     * Retries RegEnumValueEx() MAX_ATTEMPTS times before giving up.
     */
    private static byte[] WindowsRegEnumValue1(int hKey, int valueIndex, 
                                      int maxValueNameLength) {
        byte[] result = WindowsRegEnumValue(hKey, valueIndex, 
                                                            maxValueNameLength);
        if (result != null) { 
                return result;
            } else {    
                long sleepTime = INIT_SLEEP_TIME;
                for (int i = 0; i < MAX_ATTEMPTS; i++) {
                try {
                    Thread.sleep(sleepTime);
                } catch(InterruptedException e) {
                    return result;
                }
                sleepTime *= 2;
                result = WindowsRegEnumValue(hKey, valueIndex, 
                                                            maxValueNameLength);
                if (result != null) { 
                return result;
                }
            }
        }
        return result;                
    }    
    
    /**
     * Constructs a <tt>WindowsPreferences</tt> node, creating underlying
     * Windows registry node and all its Windows parents, if they are not yet 
     * created.
     * Logs a warning message, if Windows Registry is unavailable.
     */
    private WindowsPreferences(WindowsPreferences parent, String name) {
        super(parent, name);    
        int parentNativeHandle = parent.openKey(KEY_CREATE_SUB_KEY, KEY_READ);
        if (parentNativeHandle == NULL_NATIVE_HANDLE) {
            // if here, openKey failed and logged 
            isBackingStoreAvailable = false;
            return;
        }    
        int[] result = 
               WindowsRegCreateKeyEx1(parentNativeHandle, toWindowsName(name));
        if (result[ERROR_CODE] != ERROR_SUCCESS) {
            logger().warning("Could not create windows registry "
            + "node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) +
            ". Windows RegCreateKeyEx(...) returned error code " + 
            result[ERROR_CODE] + ".");
            isBackingStoreAvailable = false;
            return;
        }    
        newNode = (result[DISPOSITION] == REG_CREATED_NEW_KEY);
        closeKey(parentNativeHandle);
        closeKey(result[NATIVE_HANDLE]);        
    }

    /**
     * Constructs a root node creating the underlying
     * Windows registry node and all of its parents, if they have not yet been 
     * created.
     * Logs a warning message, if Windows Registry is unavailable.
     * @param rootNativeHandle Native handle to one of Windows top level keys.
     * @param rootDirectory Path to root directory, as a byte-encoded string.
     */    
    private  WindowsPreferences(int rootNativeHandle, byte[] rootDirectory) {
        super(null,"");
        int[] result = 
                WindowsRegCreateKeyEx1(rootNativeHandle, rootDirectory);
        if (result[ERROR_CODE] != ERROR_SUCCESS) {
            logger().warning("Could not open/create prefs root node " +
            byteArrayToString(windowsAbsolutePath()) + " at root 0x" + 
            Integer.toHexString(rootNativeHandle()) +
            ". Windows RegCreateKeyEx(...) returned error code " + 
            result[ERROR_CODE] + ".");
            isBackingStoreAvailable = false;
            return;
        }
        // Check if a new node
        newNode = (result[DISPOSITION] == REG_CREATED_NEW_KEY);
        closeKey(result[NATIVE_HANDLE]);
    }                

    /**
     * Returns Windows absolute path of the current node as a byte array.
     * Java "/" separator is transformed into Windows "\".
     * @see Preferences#absolutePath()
     */    
    private byte[] windowsAbsolutePath() {
        ByteArrayOutputStream bstream = new ByteArrayOutputStream();
        bstream.write(WINDOWS_ROOT_PATH, 0, WINDOWS_ROOT_PATH.length-1);
        StringTokenizer tokenizer = new StringTokenizer(absolutePath(),"/");
        while (tokenizer.hasMoreTokens()) {
            bstream.write((byte)'\\');
            String nextName = tokenizer.nextToken();
            byte[] windowsNextName = toWindowsName(nextName);
            bstream.write(windowsNextName, 0, windowsNextName.length-1);
        }
        bstream.write(0);
        return bstream.toByteArray();
    }

    /**
     * Opens current node's underlying Windows registry key using a 
     * given security mask.
     * @param securityMask Windows security mask.
     * @return Windows registry key's handle.
     * @see #openKey(byte[], int)
     * @see #openKey(int, byte[], int)    
     * @see #closeKey(int)    
     */
    private int openKey(int securityMask) {
        return openKey(securityMask, securityMask);
    }

    /**
     * Opens current node's underlying Windows registry key using a 
     * given security mask.
     * @param mask1 Preferred Windows security mask.
     * @param mask2 Alternate Windows security mask.
     * @return Windows registry key's handle.
     * @see #openKey(byte[], int)
     * @see #openKey(int, byte[], int)    
     * @see #closeKey(int)    
     */
    private int openKey(int mask1, int mask2) {
        return openKey(windowsAbsolutePath(), mask1,  mask2);
    }

     /**
     * Opens Windows registry key at a given absolute path using a given
     * security mask.
     * @param windowsAbsolutePath Windows absolute path of the
     *        key as a byte-encoded string.
     * @param mask1 Preferred Windows security mask.
     * @param mask2 Alternate Windows security mask.
     * @return Windows registry key's handle.
     * @see #openKey(int)
     * @see #openKey(int, byte[],int)
     * @see #closeKey(int)        
     */    
    private int openKey(byte[] windowsAbsolutePath, int mask1, int mask2) {
        /*  Check if key's path is short enough be opened at once
            otherwise use a path-splitting procedure */
        if (windowsAbsolutePath.length <= MAX_WINDOWS_PATH_LENGTH + 1) {
             int[] result = WindowsRegOpenKey1(rootNativeHandle(),
                                               windowsAbsolutePath, mask1);
             if (result[ERROR_CODE] == ERROR_ACCESS_DENIED && mask2 != mask1)
                 result = WindowsRegOpenKey1(rootNativeHandle(),
                                             windowsAbsolutePath, mask2);

             if (result[ERROR_CODE] != ERROR_SUCCESS) {
                logger().warning("Could not open windows "
                + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
                " at root 0x" + Integer.toHexString(rootNativeHandle()) + 
                ". Windows RegOpenKey(...) returned error code " + 
                result[ERROR_CODE] + ".");
                result[NATIVE_HANDLE] = NULL_NATIVE_HANDLE;
                if (result[ERROR_CODE] == ERROR_ACCESS_DENIED) {
                    throw new SecurityException("Could not open windows "
                + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
                " at root 0x" + Integer.toHexString(rootNativeHandle()) + 
                ": Access denied");
                }
             }        
             return result[NATIVE_HANDLE];         
        } else {
            return openKey(rootNativeHandle(), windowsAbsolutePath, mask1, mask2);
        }    
    }    
    
     /**
     * Opens Windows registry key at a given relative path 
     * with respect to a given Windows registry key.
     * @param windowsAbsolutePath Windows relative path of the
     *        key as a byte-encoded string.
     * @param nativeHandle handle to the base Windows key.
     * @param mask1 Preferred Windows security mask.
     * @param mask2 Alternate Windows security mask.
     * @return Windows registry key's handle.
     * @see #openKey(int)
     * @see #openKey(byte[],int)
     * @see #closeKey(int)        
     */    
    private int openKey(int nativeHandle, byte[] windowsRelativePath, 
                        int mask1, int mask2) {
    /* If the path is short enough open at once. Otherwise split the path */
        if (windowsRelativePath.length <= MAX_WINDOWS_PATH_LENGTH + 1 ) {
             int[] result = WindowsRegOpenKey1(nativeHandle,
                                               windowsRelativePath, mask1);
             if (result[ERROR_CODE] == ERROR_ACCESS_DENIED && mask2 != mask1)
                 result = WindowsRegOpenKey1(nativeHandle,
                                             windowsRelativePath, mask2);

             if (result[ERROR_CODE] != ERROR_SUCCESS) {
                logger().warning("Could not open windows "
                + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
                " at root 0x" + Integer.toHexString(nativeHandle) + 
                ". Windows RegOpenKey(...) returned error code " + 
                result[ERROR_CODE] + ".");
                result[NATIVE_HANDLE] = NULL_NATIVE_HANDLE;
             }        
             return result[NATIVE_HANDLE];         
        } else {
            int separatorPosition = -1;
            // Be greedy - open the longest possible path 
            for (int i = MAX_WINDOWS_PATH_LENGTH; i > 0; i--) {
                if (windowsRelativePath[i] == ((byte)'\\')) {
                    separatorPosition = i;
                    break;
                }
            }    
            // Split the path and do the recursion
            byte[] nextRelativeRoot = new byte[separatorPosition+1];
            System.arraycopy(windowsRelativePath, 0, nextRelativeRoot,0,
                                                      separatorPosition);
            nextRelativeRoot[separatorPosition] = 0;
            byte[] nextRelativePath = new byte[windowsRelativePath.length -
                                      separatorPosition - 1];
            System.arraycopy(windowsRelativePath, separatorPosition+1, 
                             nextRelativePath, 0, nextRelativePath.length);
            int nextNativeHandle = openKey(nativeHandle, nextRelativeRoot,
                                           mask1, mask2);
            if (nextNativeHandle == NULL_NATIVE_HANDLE) {
                return NULL_NATIVE_HANDLE;
            }    
            int result = openKey(nextNativeHandle, nextRelativePath,
                                 mask1,mask2);
            closeKey(nextNativeHandle);
            return result;
        }    
    }                

     /**
     * Closes Windows registry key.
     * Logs a warning if Windows registry is unavailable.
     * @param key's Windows registry handle.
     * @see #openKey(int)
     * @see #openKey(byte[],int)
     * @see #openKey(int, byte[],int)    
    */    
    private void closeKey(int nativeHandle) {
        int result = WindowsRegCloseKey(nativeHandle);
        if (result != ERROR_SUCCESS) {
            logger().warning("Could not close windows "
            + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) + 
            ". Windows RegCloseKey(...) returned error code " + result + ".");                 
        }
    }
    
     /**
     * Implements <tt>AbstractPreferences</tt> <tt>putSpi()</tt> method.
     * Puts name-value pair into the underlying Windows registry node.
     * Logs a warning, if Windows registry is unavailable.
     * @see #getSpi(String)
     */    
    protected void putSpi(String javaName, String value) {
    int nativeHandle = openKey(KEY_SET_VALUE);
    if (nativeHandle == NULL_NATIVE_HANDLE) {
        isBackingStoreAvailable = false;
        return;
    }
    int result =  WindowsRegSetValueEx1(nativeHandle, 
                          toWindowsName(javaName), toWindowsValueString(value));
    if (result != ERROR_SUCCESS) {
        logger().warning("Could not assign value to key " +
        byteArrayToString(toWindowsName(javaName))+ " at Windows registry node " 
       + byteArrayToString(windowsAbsolutePath()) + " at root 0x" 
       + Integer.toHexString(rootNativeHandle()) + 
       ". Windows RegSetValueEx(...) returned error code " + result + ".");
        isBackingStoreAvailable = false;
        }
    closeKey(nativeHandle);
    }   
    
    /**
     * Implements <tt>AbstractPreferences</tt> <tt>getSpi()</tt> method.
     * Gets a string value from the underlying Windows registry node.
     * Logs a warning, if Windows registry is unavailable.
     * @see #putSpi(String, String)
     */    
    protected String getSpi(String javaName) { 
    int nativeHandle = openKey(KEY_QUERY_VALUE);
    if (nativeHandle == NULL_NATIVE_HANDLE) {
        return null;
    }
    Object resultObject =  WindowsRegQueryValueEx(nativeHandle, 
                                                  toWindowsName(javaName));
    if (resultObject == null) {
        closeKey(nativeHandle);
        return null;
    }    
    closeKey(nativeHandle);
    return toJavaValueString((byte[]) resultObject);
    }

    /**
     * Implements <tt>AbstractPreferences</tt> <tt>removeSpi()</tt> method.
     * Deletes a string name-value pair from the underlying Windows registry 
     * node, if this value still exists.
     * Logs a warning, if Windows registry is unavailable or key has already
     * been deleted.
     */        
    protected void removeSpi(String key) { 
        int nativeHandle = openKey(KEY_SET_VALUE);
        if (nativeHandle == NULL_NATIVE_HANDLE) {
        return;
        }
        int result = 
            WindowsRegDeleteValue(nativeHandle, toWindowsName(key));
        if (result != ERROR_SUCCESS && result != ERROR_FILE_NOT_FOUND) {
            logger().warning("Could not delete windows registry "
            + "value " + byteArrayToString(windowsAbsolutePath())+ "\\" + 
            toWindowsName(key) + " at root 0x" + 
            Integer.toHexString(rootNativeHandle()) +
            ". Windows RegDeleteValue(...) returned error code " + 
            result + ".");
            isBackingStoreAvailable = false;
        } 
        closeKey(nativeHandle);
    }

    /**
     * Implements <tt>AbstractPreferences</tt> <tt>keysSpi()</tt> method.
     * Gets value names from the underlying Windows registry node.
     * Throws a BackingStoreException and logs a warning, if 
     * Windows registry is unavailable.
     */        
    protected String[] keysSpi() throws BackingStoreException{
        // Find out the number of values
        int nativeHandle = openKey(KEY_QUERY_VALUE);
        if (nativeHandle == NULL_NATIVE_HANDLE) {
            throw new BackingStoreException("Could not open windows"
            + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) + ".");
        }
        int[] result =  WindowsRegQueryInfoKey1(nativeHandle);
        if (result[ERROR_CODE] != ERROR_SUCCESS) {
            String info = "Could not query windows"
            + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) +
            ". Windows RegQueryInfoKeyEx(...) returned error code " + 
            result[ERROR_CODE] + ".";
            logger().warning(info);
            throw new BackingStoreException(info);
        }    
        int maxValueNameLength = result[MAX_VALUE_NAME_LENGTH];
        int valuesNumber = result[VALUES_NUMBER];
        if (valuesNumber == 0) {
            closeKey(nativeHandle);
            return new String[0];
       }
       // Get the values
       String[] valueNames = new String[valuesNumber];
       for (int i = 0; i < valuesNumber; i++) {
            byte[] windowsName = WindowsRegEnumValue1(nativeHandle, i, 
                                                        maxValueNameLength+1);
            if (windowsName == null) {
                String info = 
                "Could not enumerate value #" + i + "  of windows node " + 
                byteArrayToString(windowsAbsolutePath()) + " at root 0x" + 
                Integer.toHexString(rootNativeHandle()) + ".";
                logger().warning(info);
                throw new BackingStoreException(info);
            }
            valueNames[i] = toJavaName(windowsName);
        }
        closeKey(nativeHandle);
        return valueNames;    
    }

    /**
     * Implements <tt>AbstractPreferences</tt> <tt>childrenNamesSpi()</tt> method.
     * Calls Windows registry to retrive children of this node.
     * Throws a BackingStoreException and logs a warning message, 
     * if Windows registry is not available.
     */        
    protected String[] childrenNamesSpi() throws BackingStoreException {
        // Open key
        int nativeHandle = openKey(KEY_ENUMERATE_SUB_KEYS| KEY_QUERY_VALUE);
        if (nativeHandle == NULL_NATIVE_HANDLE) {
            throw new BackingStoreException("Could not open windows"
            + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) + ".");
        }        
        // Get number of children
        int[] result =  WindowsRegQueryInfoKey1(nativeHandle);
        if (result[ERROR_CODE] != ERROR_SUCCESS) {
            String info = "Could not query windows"
            + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) +
            ". Windows RegQueryInfoKeyEx(...) returned error code " + 
            result[ERROR_CODE] + ".";
            logger().warning(info);
            throw new BackingStoreException(info);
        }    
        int maxKeyLength = result[MAX_KEY_LENGTH];
        int subKeysNumber = result[SUBKEYS_NUMBER];
        if (subKeysNumber == 0) {
            closeKey(nativeHandle);
            return new String[0];
        }
        String[] subkeys = new String[subKeysNumber];
        String[] children = new String[subKeysNumber];
        // Get children
        for (int i = 0; i < subKeysNumber; i++) {
            byte[] windowsName = WindowsRegEnumKeyEx1(nativeHandle, i, 
                                                                maxKeyLength+1);
            if (windowsName == null) {
                String info = 
                "Could not enumerate key #" + i + "  of windows node " + 
                byteArrayToString(windowsAbsolutePath()) + " at root 0x" + 
                Integer.toHexString(rootNativeHandle()) + ". ";
                logger().warning(info);
                throw new BackingStoreException(info);
            }
            String javaName = toJavaName(windowsName);
            children[i] = javaName;
        }
        closeKey(nativeHandle);
        return children;
    }

    /**
     * Implements <tt>Preferences</tt> <tt>flush()</tt> method.
     * Flushes Windows registry changes to disk.
     * Throws a BackingStoreException and logs a warning message if Windows
     * registry is not available.
     */        
    public void flush() throws BackingStoreException{
       
	if (isRemoved()) {
	    parent.flush();
	    return;
	}
        if (!isBackingStoreAvailable) {
            throw new BackingStoreException(
                                       "flush(): Backing store not available.");
        }
        int nativeHandle = openKey(KEY_READ);
        if (nativeHandle == NULL_NATIVE_HANDLE) {
            throw new BackingStoreException("Could not open windows"
            + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) + ".");
        }
        int result = WindowsRegFlushKey1(nativeHandle);
        if (result != ERROR_SUCCESS) {
            String info = "Could not flush windows "
            + "registry node " + byteArrayToString(windowsAbsolutePath()) 
            + " at root 0x" + Integer.toHexString(rootNativeHandle()) + 
            ". Windows RegFlushKey(...) returned error code " + result + ".";
            logger().warning(info);
            throw new BackingStoreException(info);
        }                
        closeKey(nativeHandle);
    }
    

    /**
     * Implements <tt>Preferences</tt> <tt>sync()</tt> method.
     * Flushes Windows registry changes to disk. Equivalent to flush().
     * @see flush()
     */        
    public void sync() throws BackingStoreException{
        if (isRemoved())
            throw new IllegalStateException("Node has been removed");         
        flush();
    }

    /**
     * Implements <tt>AbstractPreferences</tt> <tt>childSpi()</tt> method.
     * Constructs a child node with a 
     * given name and creates its underlying Windows registry node, 
     * if it does not exist.
     * Logs a warning message, if Windows Registry is unavailable.
     */        
    protected AbstractPreferences childSpi(String name) {
            return new WindowsPreferences(this, name);
    }

    /**
     * Implements <tt>AbstractPreferences</tt> <tt>removeNodeSpi()</tt> method.
     * Deletes underlying Windows registry node.
     * Throws a BackingStoreException and logs a warning, if Windows registry
     * is not available.
     */        
    public void removeNodeSpi() throws BackingStoreException {
        int parentNativeHandle = 
                         ((WindowsPreferences)parent()).openKey(DELETE);
        if (parentNativeHandle == NULL_NATIVE_HANDLE) {
            throw new BackingStoreException("Could not open parent windows"
            + "registry node of " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) + ".");
        }
        int result = 
                WindowsRegDeleteKey(parentNativeHandle, toWindowsName(name()));
        if (result != ERROR_SUCCESS) {
            String info = "Could not delete windows "
            + "registry node " + byteArrayToString(windowsAbsolutePath()) + 
            " at root 0x" + Integer.toHexString(rootNativeHandle()) +
            ". Windows RegDeleteKeyEx(...) returned error code " + 
            result + ".";
            logger().warning(info);
            throw new BackingStoreException(info);
        }
        closeKey(parentNativeHandle);
    }

    /**
     * Converts value's or node's name from its byte array representation to
     * java string. Two encodings, simple and altBase64 are used. See
     * {@link #toWindowsName(String) toWindowsName()} for a detailed 
     * description of encoding conventions.
     * @param windowsNameArray Null-terminated byte array.
     */         
    private static String toJavaName(byte[] windowsNameArray) {
        String windowsName = byteArrayToString(windowsNameArray);
        // check if Alt64
        if ((windowsName.length()>1) && 
                                   (windowsName.substring(0,2).equals("/!"))) {
            return toJavaAlt64Name(windowsName);
        }
        StringBuffer javaName = new StringBuffer();
        char ch;
        // Decode from simple encoding
        for (int i = 0; i < windowsName.length(); i++){
            if ((ch = windowsName.charAt(i)) == '/') {
                char next = ' ';
                if ((windowsName.length() > i + 1) && 
                   ((next = windowsName.charAt(i+1)) >= 'A') && (next <= 'Z')) {
                ch = next;
                i++;
                } else  if ((windowsName.length() > i + 1) && (next == '/')) {
                ch = '\\';
                i++;
                }
            } else if (ch == '\\') {
                ch = '/';
            }
            javaName.append(ch);
        }
        return javaName.toString();
    }
    
    /**
     * Converts value's or node's name from its Windows representation to java
     * string, using altBase64 encoding. See
     * {@link #toWindowsName(String) toWindowsName()} for a detailed 
     * description of encoding conventions.
     */         
    
    private static String toJavaAlt64Name(String windowsName) {
        byte[] byteBuffer = 
                          Base64.altBase64ToByteArray(windowsName.substring(2));
        StringBuffer result = new StringBuffer();
        for (int i = 0; i < byteBuffer.length; i++) {
            int firstbyte = (byteBuffer[i++] & 0xff);
            int secondbyte =  (byteBuffer[i] & 0xff);
            result.append((char)((firstbyte << 8) + secondbyte));
        }
        return result.toString();
    }    

    /**
     * Converts value's or node's name to its Windows representation
     * as a byte-encoded string.
     * Two encodings, simple and altBase64 are used.
     * <p>
     * <i>Simple</i> encoding is used, if java string does not contain
     * any characters less, than 0x0020, or greater, than 0x007f.
     * Simple encoding adds "/" character to capital letters, i.e.
     * "A" is encoded as "/A". Character '\' is encoded as '//', 
     * '/' is encoded as '\'.
     * The constructed string is converted to byte array by truncating the
     * highest byte and adding the terminating <tt>null</tt> character.
     * <p>
     * <i>altBase64</i>  encoding is used, if java string does contain at least 
     * one character less, than 0x0020, or greater, than 0x007f.
     * This encoding is marked by setting first two bytes of the
     * Windows string to '/!'. The java name is then encoded using 
     * byteArrayToAltBase64() method from 
     * Base64 class.
     */         
    private static byte[] toWindowsName(String javaName) {
        StringBuffer windowsName = new StringBuffer();
        for (int i = 0; i < javaName.length(); i++) {
            char ch =javaName.charAt(i);
            if ((ch < 0x0020)||(ch > 0x007f)) {
                // If a non-trivial character encountered, use altBase64
                return toWindowsAlt64Name(javaName);
            }
            if (ch == '\\') {
                windowsName.append("//");
            } else if (ch == '/') {
                windowsName.append('\\');
            } else if ((ch >= 'A') && (ch <='Z')) {
                windowsName.append("/" + ch);
            } else {
                windowsName.append(ch);
            }
        }
        return stringToByteArray(windowsName.toString());
    }

    /**
     * Converts value's or node's name to its Windows representation
     * as a byte-encoded string, using altBase64 encoding. See
     * {@link #toWindowsName(String) toWindowsName()} for a detailed 
     * description of encoding conventions.
     */         
    private static byte[] toWindowsAlt64Name(String javaName) {
        byte[] javaNameArray = new byte[2*javaName.length()];
        // Convert to byte pairs
        int counter = 0;
        for (int i = 0; i < javaName.length();i++) {
            	int ch = javaName.charAt(i);
                javaNameArray[counter++] = (byte)(ch >>> 8);
	        javaNameArray[counter++] = (byte)ch; 
        }
    
        return stringToByteArray(
                           "/!" + Base64.byteArrayToAltBase64(javaNameArray));
    }

    /**
     * Converts value string from its Windows representation
     * to java string.  See
     * {@link #toWindowsValueString(String) toWindowsValueString()} for the
     * description of the encoding algorithm.
     */         
     private static String toJavaValueString(byte[] windowsNameArray) {
        // Use modified native2ascii algorithm
        String windowsName = byteArrayToString(windowsNameArray);
        StringBuffer javaName = new StringBuffer();
        char ch;
        for (int i = 0; i < windowsName.length(); i++){
            if ((ch = windowsName.charAt(i)) == '/') {
                char next = ' ';
                
                if (windowsName.length() > i + 1 && 
                                    (next = windowsName.charAt(i + 1)) == 'u') {
                    if (windowsName.length() < i + 6){
                        break;
                    } else {
                        ch = (char)Integer.parseInt
                                      (windowsName.substring(i + 2, i + 6), 16);
                        i += 5;
                    }
                } else  
                if ((windowsName.length() > i + 1) && 
                          ((windowsName.charAt(i+1)) >= 'A') && (next <= 'Z')) {
                ch = next;
                i++;
                } else  if ((windowsName.length() > i + 1) && 
                                               (next == '/')) {
                ch = '\\';
                i++;
                }
            } else if (ch == '\\') {
                ch = '/';
            }
            javaName.append(ch);
        }
        return javaName.toString();
    }    

    /**
     * Converts value string to it Windows representation.
     * as a byte-encoded string.
     * Encoding algorithm adds "/" character to capital letters, i.e.
     * "A" is encoded as "/A". Character '\' is encoded as '//', 
     * '/' is encoded as  '\'.
     * Then encoding scheme similar to jdk's native2ascii converter is used
     * to convert java string to a byte array of ASCII characters.
     */         
    private static byte[] toWindowsValueString(String javaName) {
        StringBuffer windowsName = new StringBuffer();
        for (int i = 0; i < javaName.length(); i++) {
            char ch =javaName.charAt(i);
            if ((ch < 0x0020)||(ch > 0x007f)){
                // write \udddd
                windowsName.append("/u");
                String hex = Integer.toHexString(javaName.charAt(i));
                StringBuffer hex4 = new StringBuffer(hex);
                hex4.reverse();
                int len = 4 - hex4.length();
                for (int j = 0; j < len; j++){
                    hex4.append('0');
                }
                for (int j = 0; j < 4; j++){
                    windowsName.append(hex4.charAt(3 - j));
                }
            } else if (ch == '\\') {
                windowsName.append("//");
            } else if (ch == '/') {
                windowsName.append('\\');
            } else if ((ch >= 'A') && (ch <='Z')) {
                windowsName.append("/" + ch);
            } else {
                windowsName.append(ch);
            }
        }
        return stringToByteArray(windowsName.toString());
    }
    
    /**
     * Returns native handle for the top Windows node for this node.
     */
    private int rootNativeHandle() {
        return (isUserNode()? USER_ROOT_NATIVE_HANDLE :
                              SYSTEM_ROOT_NATIVE_HANDLE); 
    }
    
    /**
     * Returns this java string as a null-terminated byte array
     */
    private static byte[] stringToByteArray(String str) {
        byte[] result = new byte[str.length()+1];
        for (int i = 0; i < str.length(); i++) {
            result[i] = (byte) str.charAt(i);
        }    
        result[str.length()] = 0; 
        return result;
    }
    
    /** 
     * Converts a null-terminated byte array to java string
     */
    private static String byteArrayToString(byte[] array) {
        StringBuffer result = new StringBuffer();
        for (int i = 0; i < array.length - 1; i++) {
            result.append((char)array[i]);
        }    
        return result.toString();
    }
    
   /** 
    * Empty, never used implementation  of AbstractPreferences.flushSpi(). 
    */
    protected void flushSpi() throws BackingStoreException {
        // assert false;
    }
    
   /** 
    * Empty, never used implementation  of AbstractPreferences.flushSpi(). 
    */
    protected void syncSpi() throws BackingStoreException {
        // assert false;
    }

    private static synchronized Logger logger() {
        if (logger == null) {
            logger = Logger.getLogger("java.util.prefs");
        }
        return logger;
    }
}
